Comments

I'm one of the regulars from the "BreakTime" site - Fine Homebuilding's message board. They suggested I post over here since this question is more up your alley.

I'm looking at possibly buying a house that has a steam boiler from the 1950s. I asked a local HVAC guy about replacing it with a new gas forced air unit that would be more efficient. He told me steam units were inherently more efficient, and there would be no savings in installing a new furnace.

This doesn't sound right to me - I don't see how something from the 1950s could be anywhere NEAR as efficient as a modern furnace. But I'm also not an expert on the subject.

Any thoughts would be appreciated. Here's a link to the thread at BreakTime if you're interested:

You have to consider heat as a SYSTEM--not just the heating appliance.

While a modern condensing forced air furnace itself will be more efficient than any steam boiler, it is in the DELIVERY of this heat to the structure where steam and water systems are inherently more efficient.

Even the best ductwork in new construction is very leaky compared to hydronic systems. Many forced air retrofits are extraordinarily leaky.

If you reply with the make and model of the boiler the steam gurus here will be glad to give you an idea of its efficiency and whether or not a replacement will do much to increase it. Since no steam boilers can recover waste heat by condensing flue gasses, they have a definite limit on efficiency and some of the older models are likely nearly as efficient as new ones.

You'll spend alot less with a top of the line forced air system, condensing and DC blower, sealed ductwork in the basement, there is no way a steam system can have a good seasonal effeciency since it must always bring the boiler and pipes up to temp before any heat is released. So, if you had 2 identical houses the modern warm air would always use less fuel at the same indoor set temp. There are some people at this site who can make the steam system work as designed but it's still a turn of the century design. The best you can do with the brand new steam boiler running is about 80 percent combustion effecieny. Your 1950 boiler is probably abuot 60%. As to whether you should change that's a different story, perhaps you see the cast iron rads as art objects, perhaps you like the comfort of a 200 degree surface temp block of iron, some people do. And, you have the other choice of converting the steam to hot water if you want control and comfort and fuel savings. You may decide to stay with steam but don't con youself that it's a fuel efeciency choice.

...of confusion regarding efficiencies. Combustion eff is NOT boiler (or furnace) eff. It seems nobody in the residential heating industry uses the eff calculation that is used for industrial boilers, which is net heat out, divided by heat of the fuel in, over the same time period, multiplied by 100. To do this with residential steam/hot water boilers, and forced air units is not very practical in the field, as the instrumentation would likely cost more than the heating plant. However, this could EASILY be done in labs, by the government or overseeing bodies, and/or manufacturers. This kind of efficiency calculation provides the "big picture", encompassing skin losses, stack losses, combustion ineffeciencies, etc. And it's an apples-to-apples value that can be applied to compare ALL kinds of heating equipment. The rationale of how the AFUE number came to be, and why it's used, continues to baffle me. I've asked questions here before about the AFUE number, pointedly directed at manufacurers - not much in the way of any effective response. I think it's a grossly over-complex calculation that is designed to confuse, rather inform the public at large. Every time I see a calculation for anything that is overly complicated, a little alarm bell goes off in my head, and I wonder "What ARE these people trying to hide?" I need to be careful not to tar all manufacturers with the same brush. I suspect that a lot of them know that the efficiency calculations being published are, well, not rooted in reality. The method is mandated by the government rules and regulations, so even those that disagree have to go along with it.

Don't con yourself that the AFUE efficiency rating values applied to ANY of these units has any particular relationship to it's actual efficiency, because it doesn't. It's little more than an arbitrary number assigned for comparison purposes only. "Your actual milage may vary." Caveat emptor.

Scorched-air is a lousy choice for heating. The moving air makes you feel cold, so you end up raising the thermostat to compensate.

And speaking of ducts- have you ever looked inside one after it's been in place for a few years? Very often it looks like the birth of the universe, with all kinds of exotic life-forms.

There are many boilers out there, both oil- and gas-fired, which are much more efficient than yours. But I agree that the first thing to do is insulate, weatherstrip, caulk, install storm windows and anything else that will reduce the heat loss. Then your new boiler can be smaller, since it won't have to do as much work!

Try the Find a Contractor page of this site to locate someone near you who can help you out.

Don't give up on a steam system. I used to own a house with hot water radiators, then I had a forced-air system, and now I own an old home with a 1-pipe steam system.

I had to do some work on the system to get it up to snuff when I first bought the house -- e.g., put in a new boiler, insulate the mains, and replace some of the vents, but it is now hands-down the best heat you could ever ask for. The heating bills are no more than with a water system. It doesn't dry out the air or produce dust-bunnies. It is dead silent -- you can just baaarely hear the steam come into the radiators and the new boiler is very very quiet. The heat is extremely even throughout the house and tends to stay within a nice narrow range. Once you get the hang of how to adjust the radiator vents, it's very easy to get the system in balance. (Room too warm? Go to a smaller exit vent. Room too cold? Go to a bigger one.)

The modern boilers are so much better than the historical units. You can get away with a much smaller one than was typically spec'd 25 years ago. Once certain basics are attended to, the systems are pretty much bombproof.

One huge benefit over a water system is that unless the steam is up, there is nothing in the pipes but air. No risk of a frozen pipe bursting, and no risk of damage to the home from a leaky pipe.

Once you realize how a steam system works and "breathes", I think you'll agree that it's the best way to go. By no means should it cost significantly more to run a steam system than a forced-air unit. In fact, you can typically leave the thermostat a little lower since there is more humidity in the home and as a consequence it "feels" warmer.

A 2-pipe system might be better still, I don't know! But a properly set up 1-pipe steam system is a truly elegant thing.

Efficiency is over rated. In the seventies I got a government grant to test an improvement. Fulton provided a waste heat boiler; RobertShaw, I think it was, provided the controller. So the inefficiency of the boiler was used to preheat domestic hot water. This was in a small four story apartment building. Definitely saved fuel. And probably wear on the water heater. On the other hand the chimney was colder. I can't remember how many years the payback was. Perhaps current low interest rates make such possibilities more attractive.

Forced air is the least comfortable but most folks don't seem to mind. If I was building a mansion, I'd probably go steam. With modern materials you could make it tight and almost maintenance free. On the other hand, new construction is so efficient that heating is moot.

The bottom line to me is that no matter how many wraps of tape and insulation ductwork receives, or how much fancy PVC venting is used, A steam boiler with a high-tech power burner and insulated pipes is a better quality of heating. Never Replace anything with forced air unless its a gravity furnace or an existing forced air furnace.